1. Field of the Invention
The present invention relates to an authentication apparatus authenticating an organism based on a characteristic amount acquired from the organism, and a method thereof.
2. Description of the Related Art
In communication systems communicating via a network and predetermined processing apparatuses, authentication may be performed on whether the user is authorized or not.
For such authentication, there is, for example, biological authentication in which biological data of a fingerprint, a vein and the like is read from a user, and authentication is performed based on a value of correlation between inspection characteristic data showing a characteristic specific to the user extracted from the biological data and reference characteristic data held in advance.
In such biological authentication, how to determine a threshold of a correlation value used as a criterion for determining whether the user is the genuine person or a different person is important in achievement of high reliability.
That is, a false acceptance rate (FAR) being a probability of erroneously determining a different person to be the genuine person and a false rejection rate (FRR) being a probability of erroneously determining the genuine person to be a different person are determined according to how the threshold is determined.
Methods for determining the threshold include various methods such as a method shown in, for example, Patent Document 1: Japanese Patent No. 3439359.
In this type of authentication apparatus, if an image pickup device or identification object itself is slightly changed with age, the state of a distribution of similarity degrees (checking results), which is determined to be an identification object (hereinafter referred to as similarity distribution), changes according to the change with age.
Specifically, given that ideal states of a similarity distribution when the degree of similarity between reference characteristic data and inspection characteristic data ranges from “0” to “1”, and the threshold is “0.6”, and a distribution of similarity degrees, which is determined to be not an identification object (hereinafter referred to as non-similarity distribution), are the states shown in, for example, FIG. 22, the similarity distribution goes into various states such that its average decreases as shown in, for example, FIG. 23, the distribution generally shifts toward the threshold as shown in, for example, FIG. 24, and its peak does not change but its slope becomes gentle although not shown in the figure, according to a slight change with age.
As such a change with age increases, the similarity distribution progressively shifts to a domain smaller than the threshold, and therefore in the authentication apparatus, the probability of determining a registered identification object to be a different identification object (i.e. False Rejection Ratio (FRR)) increases, resulting in a degradation in reliability of improving authentication accuracy.
As one method of countermeasures against this problem, there is a method in which independently of a threshold serving as a criterion of determining whether the object is an identification object or not, a range between an update range lower threshold and an update range upper threshold is set as an update range, whether or not the similarity degree is within the set update range is determined every time authentication is performed, and when the similarity degree is within the update range, reference characteristic data is updated (see, for example, Patent Document 1: Japanese Patent Laid-Open No. 2004-157602 (FIG. 5)).